Episode 334 Which sperm is the oldest sperm - the ancestor sperm that came before all others? Well, you might think it links back to an ancient animal that came before us, but the oldest sperm may actually predate animals altogether. We explore this plus the enduring mystery of the scrotum - and why a male’s most important body part is so delicate and…exposed. The team hears about the variation in scrotum morphology across mammals, and the evolution of “non-scrotality”. Our brains undergo four major turning points throughout our lives. New research suggests the way our brains are wired shifts at key stages as we get older - and your adolescent years may last longer than you realised. We explore what is happening at each brain stage, how long they last and why this research could prove useful in figuring out conditions like depression or dementia. Politicians, scientists, celebrities and climate activists gathered at the National Emergency Briefing in London this week and the message was clear: environmental breakdown is escalating faster than expected. One report highlighted that the biggest health risk of the 21st century is climate change, and other scientists described scenarios of starvation, wars and ungovernable societies. But there were messages of empowerment and hope too. Hear from some of the scientists - and a British army general - at the event. Hosted by Rowan Hooper and Penny Sarchet, with guests Sam Wong, Carissa Wong, Michael Le Page, Lt General Richard Nugee, Paul Behrens and Kevin Anderson. To read more about these stories, visit https://www.newscientist.com/ Sign the National Emergency Briefing open letter here: https://www.nebriefing.org/open-letter-keir Learn more about your ad choices. Visit megaphone.fm/adchoices

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“What did the council decide on item 42?” — answered with the speaker and the moment.